Typical concrete materials are made of Portland cement, sand, stone and water. When water is mixed with Portland cement, an exothermic reaction occurs, which results in a solid mass with a density approximating 145 pounds per cubic foot.
Although conventional concrete is useful for many applications, and has a long history of use, lighter weight mixes such as “autoclaved aerated concrete” (AAC) are known to have considerably lighter density than conventional concrete and also exhibit some insulating properties as well. These AAC products are limited owing to the high cost of equipment, and lengthy processing cycles. Portland cement, in fact, while widely used in many lighter weight construction applications, requires care in handling since any changes in temperature, vibration or disturbance can cause the fine cellular structure to collapse before the materials have set sufficiently to be self-supporting. Also, Portland-based cellular concretes at low densities tend to be very friable and are easily damaged, and exhibit very low compressive strength unless exposed to curing procedures common to AAC. This AAC process is time consuming, with 12 hour cycles; capital intensive, with autoclaves involved, and energy intensive, with 10 hours under steam and pressure.
Phosphate-containing concretes have been proposed for a number of purposes. For example, U.S. Pat. No. 3,960,580 describes use of oxy-boron compounds as retarders in acid-base cements containing magnesium oxide and various grades of powdered phosphate compounds. U.S. Pat. No. 4,335,060 describes an acid-base cement comprising “liquid ammonium polyphosphates” with fly ash and magnesium oxide where the fly ash can be used as a substitute for part or all of the MgO. Further references to acid-base cements include those found in U.S. Pat. Nos. 5,645,518; 5,830,815; 5,846,894 and 6,133,498, which disclose phosphate ceramics that encapsulate various types of residual materials and contaminants such as heavy metals, asbestos, ash, various wastes, and low-level radioactive waste. These patents teach the use of residual materials that act as fill materials, which are encapsulated and do not participate in the chemical reaction of the product. Such processes use high-purity reagent grade phosphates and dead burned MgO. These processes utilize expensive MKP, i.e., mono-potassium phosphate, which reacts with the P2O4 to produce high sensitivity matrices—but tend to be too expensive—when compared to the use of MAP, i.e., mono-ammonium phosphate, as an acid source. These products tend to be lighter than Portland cement concretes, but form dense matrices that are ineffective for use as insulating materials, and are not generally used in applications where-a light weight insulating material would be advantageous. U.S. Pat. No. 5,002,610 discusses use of fibre additives to magnesium phosphate cements and non-reactive fill materials to achieve mechanical properties desirable for construction uses similar to those of Portland cement-based concrete. U.S. Pat. No. 6,136,088 discloses production of a cement and/or mortar based on reactions of water, magnesium compounds, and potassium phosphate, which utilize retardants such as boron oxide, polyphosphonic acid, carboxylic acid, hydrocarboxylic acid, and salts of these acids; additives such as silica, class F fly ash, talc, clay based sand, silica fume, and mixtures of these materials are used as inert fillers; these composites are dense and have high compressive strengths.
While the prior art covers numerous applications and uses for these acid/base cements, often referred to as “Sorrell Cements,” they all create a fairly high density, solid matrix with very high compressive strengths and very low permeability. They tend to be too heavy to be considered in applications where lightweight and low thermal conductivity are crucial to the success of the intended purposes.
It is, therefore, desirable to improve the art. It is, furthermore, more particularly desirable to provide materials that address such deficiencies of the prior art as relate to thermal conductivity and overall density, cost of raw materials, and issues and shortcomings characteristic with these prior inventions. It is also desirable to provide improved compositions efficiently, and to have generally widespread use for them.